OSMOTIC COMPONENTS IN COTTON (GOSSYPIUM HIRSUTUM L.) FIBERS IN RESPONSE TO SOIL MOISTURE DEFICIT DURING FIBER EXPANSION

The present study aimed to determine how main osmotic active substances (malate, potassium and soluble sugars) in cotton fibers respond to soil drought. A pot study with two water regimes was performed in 2015 and 2016 using two cotton lines A001 and A705. The irrigated plants (control) were watered at 1-d interval with the optimum quantity of underground water determined on the basis of a gravimetric method. Drought treatment was defined as withdrawing water from pots until the leaf wilting symptom was visible, and water stressed plants were exposed to limited water supply for 25 days receiving 50% of the control irrigation at 2-d interval. Following 25 days of water deficit treatment, those plants were re-watered with the same quantity as the control. Drought induction caused a significant reduction in fiber length and strength in A001. Net photosynthetic rate (P-n), stomatal conductance (g(s)), and transpiration rate (E) in A001 and A705 were reduced significantly by soil drought indicating the present water deficit design did generate a photosynthetically physiological difference. The depressed leaf photosynthesis led to the deficient accumulation of soluble sugars, malate and potassium in water stressed fibers, and in turn to the reduced fiber length.